Molecular imaging is a relatively new and fast growing research discipline, which has the ability to study diseases non-invasively in living subjects at the molecular level. Numerous researches have demonstrated that molecular imaging techniques play a central role in the era of personalized medicine. A variety of imaging modalities have been developed for providing functional and anatomical information of diseases in living small animals and patients, which include positron emission tomography (PET), single photon emission computed tomography (SPECT), optical imaging (OI, bioluminescence and fluorescence), magnetic resonance imaging (MRI), ultrasound (US), and computed tomography (CT).
Radioactive molecular probes are traditionally imaged with PET, SPECT or gamma (γ) cameras, by taking advantages of the capability of these imaging modalities to detect the high energetic γ rays. Whereas OI generally detects low energy lights (visible or near-infrared lights) emitted from bioluminescence or fluorescence probes. So far there has not been any overlap between radioactive probes and conventional OI techniques.